Slow-moving, Fast-acting: The benefits of HVLS fans

November 13, 2017

All images courtesy of Big Ass Fans

By Vicky BroadusThe largest chain of health clubs in Canada understands the benefits of high-volume, low-speed (HVLS) overhead fans. In the last seven to eight years, Goodlife Fitness has installed them in 90 per cent of its facilities across the country, viewing the slow-moving air-circulators as an essential piece of exercise equipment.

“The fans run basically 24 hours in most places and everyone loves them,” said Lindsay Markle. Until recently, Markle was project manager with Trigon Construction Management, which—as the company’s name suggests—manages construction and renovation for Goodlife.

While HVLS fans can range in diameter from about 2159 mm (85 in.) to 7 m (24 ft), most of those installed at Goodlife facilities are in the 3-m (10-ft) range. Markle said they were brought in as an alternative to smaller industrial fans that were not doing the job. The large fans work in every season, keeping guests cool in the summer months and helping mix or ‘destratify’ the heated air that inevitably rises toward the ceiling in winter.

A place where people come for the purpose of exercising is ideally suited for HVLS fans. The constant, gentle breeze from the fans cools sweating bodies through what is known as evaporative cooling. However, almost any facility can benefit from the fans’ air circulation and energy efficiency. Since they were introduced 18 years ago, they have been installed in many kinds of industrial and commercial facilities. Further, as people become familiar with the fans’ ability to move air, they are finding the systems can replace ductwork in many places, which creates cost savings on the front end.

Building a better, bigger fanSince the electric fan was invented in the 1880s, people have relied on it for relief from the heat. The early technology was simple: spinning blades produced a high-velocity current of air that facilitated the evaporation of perspiration from the skin’s surface. This phenomenon made the person on the receiving end of the airflow feel cooler than the air temperature would indicate, and was much appreciated in settings such as the ‘sweatshops’ of the 19th and 20th centuries. However, it was clear fans that cooled one or two people were far from ideal in busy workplaces.

For more than a century, not much changed in the science of air movement; today, most fans still operate using the same principles as that very first electric fan. Then, late in the 20th century, there was a major breakthrough in technology via HVLS fans. Unlike their high-velocity relatives, which create localized cooling with a small jet of air, HVLS fans move a lot of air through the devices’ size and rotational speed. Rather than delivering a strong gust of air over a small area, the HVLS fan produces a gentle breeze over a large area. The constant circulation guarantees all the air within a space remains at a close-to-uniform temperature—in other words, there are not layers of cool, warm, and hot air between the ceiling and the floor.

The first customers for this new kind of fan were dairy farmers, who put them in barns to keep cows comfortable and productive. Soon, however, it was recognized the fans had the same effect on people working in warehouses, distribution centres, and factories. Fast-forwarding another decade of advances in technology and design, HVLS fans can now be found everywhere from fitness centres to arenas, churches to schools, and offices to homes. The energy-efficient technology makes more sense every year as the world tries to reduce reliance on traditional power sources.

The nuts and bolts of air movementThe use of aerodynamically designed airfoils and small, energy-efficient motors allows HVLS fans to move huge volumes of air very slowly over very large areas. How exactly does it all work? The airflow from an HVLS fan heads to the floor in a column equivalent to the fan’s diameter. When the air reaches the floor, it spreads out in all directions until it hits a wall or other large obstruction, such as warehouse racking, at which point it moves up, around, and back across the ceiling to the fan.

A single 7-m (24-ft) diameter ceiling fan can cover 1858 to 2787 m2 (20,000 to 30,000 sf) from a ceiling height of up to 14 m (45 ft). In larger open spaces, multiple fans work in tandem—as the pressure front from one fan spreads out along the floor, it meets a similarly expanding jet of air coming from the other fan. These jets collide and deflect up toward the ceiling in the same way air moves when encountering a wall. The result of this is each fan behaves as though it is operating alone in a space smaller than the actual geometry of the room, thereby increasing high-speed airflow coverage within the space.

By moving a lot of air very slowly—at about 5 km/h (3 mph) or so—the HVLS fan creates quieter, less disruptive airflow that cools a far greater area than a high-velocity fan, and does it very efficiently. The average daily operating cost of a good-quality large-diameter fan is a few dollars.

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